This invention relates generally to a semiconductor integrated circuit device (hereinafter called an "IC"), and more particularly to a technique which is suitable when used for a semi-custom gate array IC.
Gate arrays have been drawing increasing attention in recent years as one of the types of semi-custom ICs which make it possible to efficiently produce an LSI in accordance with a user's requirement.
A gate array is an IC that constitutes a desired logic circuit by extending wiring on a base chip (a semiconductor substrate on which a large number of circuit elements are fabricated in advance).
Hitachi, Ltd. has developed a large-scale gate array in which the number of gates of an internal logic circuit is several thousand. This IC is equipped with buffer circuits having a level conversion function at the input-output portions thereof so that the IC can be connected to various systems.
As a result of studies, the inventors of the present invention have found that elements in an input buffer circuit are likely to be damaged by an external surge voltage. This invention is completed in order to cope with such a problem.